Conventionally, as engine lubrication systems, there exist for example, an engine lubrication system as disclosed in JP-A-10-339124 in which a lubricating oil pump is directly attached to an end of a crankshaft and an engine lubrication system as disclosed in JP-UM-A-5-52205 in which a lubricating oil pump is disposed at an end of a crankshaft with a pump shaft of the pump being connected to the crankshaft via a coupling piece.
In the lubrication system in which the lubricating oil pump is directly connected to the end of the crankshaft, in the event that the center of the crankshaft oscillates, this constitutes a direct cause of the sway of an inner rotor of the lubricating oil pump, leading to the reduction in durability of the lubricating oil pump. Due to this, the lubricating oil pump needs to be disposed at a position as close to a bearing portion of the crankshaft as possible, and hence there is caused a problem of narrowing the degree of freedom in selecting where to dispose the lubricating oil pump.
In addition, in the lubrication system in which the crankshaft and the pump shaft are connected together with the coupling piece, since a discharge port of the pump is made to communicate directly with an oil supply passageway formed in the coupling piece along the axial center thereof, there is caused a problem that an oil filter is difficult to be disposed on a discharge side of the lubricating pump.
The invention was made in view of the problems inherent in the conventional systems, and an object thereof is to provide an engine lubrication system which can avoid the influence of the deflection of the crankshaft, which can enhance the degree of freedom in selecting where to dispose a lubricating oil pump and which has a high degree of freedom in design where, for example, an oil filter is disposed on a discharge side of the lubricating oil pump.